This invention relates generally to a method of controlling the quantity of a lubricating oil in or for an internal mixer and, more particularly to a method of controlling the quantity of a lubricating oil for an internal mixer in which the temperature generated at a seal ring of a dust seal portion is detected and a lubricating oil is supplied to a seal surface in a quantity corresponding to the generated temperature.
In a conventional rubber mixer, a dust seal portion for supporting the shaft portion of a kneading rotor of the mixer is likely to generate heat due to presence in gaps of matters such as carbon, powder, rubber and so forth, and a sliding surface is also likely to become coarse. When the sliding surface becomes coarse, it results in the problem such as leaking of carbon, and the mixer must be stopped for an extended period of time in order to replace the component and to adjust the machine. To prevent this problem, a mechanical seal has heretofore been used in the dust seal portion and a large quantity of a lubricating oil is supplied to the mechanical seal portion.
The feed quantity of the lubricating oil is set in accordance with the heat generation condition of the seal ring. Generally, the temperature of the seal ring varies from room temperature to above 80.degree. C., and the factors that are involved with the heat generation are the rotation of a rotor, the kinds of mixtures, the feed sequence of materials, and a ground internal pressure which is generally from 2 to 3 kg/cm.sup.2, but which may reach a peak of 10-20 kg/cm.sup.2, and these factors change continually. The heat generation condition also widely changes depending upon the solubility of chemicals or matters in gaps.
For reasons described above, it has been necessary in the past to set the oil quantity to the level that is necessary at the time of the highest heat generation.
The below table illustrates temperatures of the seal ring in accordance with ordinary materials to be kneaded.
______________________________________ number of seal ring product notches temperature ______________________________________ 1 matter kneaded NR type 6 60.about.80.degree. C. in the 1st step 2 matter kneaded SBR type 4 40.about.60.degree. C. in the 1st step 3 matter kneaded 2 25.about.40.degree. C. in one-step kneading ______________________________________ Notes: Products 1 and 2 are those kneaded in the 1st one of a multistep kneading The term "number of notches" means the number of adjustment knobs for the pump discharge quantity, 8 being the maximum. The term "onestep" means those rubbers of which the kneading can be done in a single step.
When the feed quantity of the lubricating oil is set in accordance with the highest heat generation of the seal ring as described above, the feed quantity tends to be greater than necessary. In other words, the lubricating oil is consumed in a greater quantity than necessary.
A proposal has been made in which a pump motor for supplying the lubricating oil is variable in order to select a suitable rotation of the pump in accordance with the rotation of the rotor. However, this proposal does not directly cope with the problem of the generated heat of or in the seal ring. Moreover, it is that a temperature rise does not take place immediately after the start of mixing but takes place only after mixing of several to some dozens of batches in the mixer. Therefore, the oil quantity cannot be reduced even at the time of a low heat generation and the lubricating oil has to be used in quantities more than necessary, in the same way as above described.